Picture centering control apparatus



llama. 5, 3 A. N. GOLDSMITH PICTURE CENTERING CONTROL APPARATUS Filed June 28, 1941 U 7 A w W 1 6 0 R mm NA W F M% L 0 INVENTOR ALFRED N. GOLDSMITH A I'TORNEY arcane PICTURE omvrnnmo GDNTROL APPARATUS Alfred N. Goldsmith, New York, N. W.

Application time 28, 1941, Serial No. 400,205

8 Claims.

hiy invention relates, in general, to cathode ray apparatus, and more particularly to such apparathe for determining the position of reproduced images on the screen oi a cathode ray tube.

In presently known television receivers there are provided a number oi different hand controls such as buttons or knobs for various purposes, among these being the control for increasing or decreasing the intensity of the reproduced picture, the picture contrast control, synchronizing controls, centering controls, and the like. It therefore is highly desirable to minimize the number of these controls since each additional adjustment on a receiver is an inconvenience to the user, and may even lead to its incorrect operation and consequent dissatisfaction. Accordingly, it is one of the objects of my invention to provide an apparatus which will eliminate some of the presently known hand adjusted controls.

At the present time the reproduced imag on a cathode ray tube screen is centered by means of a fixed bias which controls the initial point of impact of the cathode ray beam on the screen, and this fixed bias is applied either in the form of a voltage in the case where the deflection is accomplished electrostatically, or a current in the case where the deflection is accomplished electromagnetically. The hand control arrangement is provided to vary the value of this bias, and hence control the centering of the picture or image. This device is undesirable because it multiplies the number of controls and places the burden of proper operation on a usually unskilled owner of the receiver. Accordingly, it is another of the objects of my invention to provide an apparatus in which the centering of the image reproduced on the screen of a cathode ray tube is accomplished automatically.

In addition to accomplishing the aforementioned objects, it is also desirable that the device be one which does not add to the bulk of the receiver or appreciably to the cost thereof, and it should be practicable as well as simple. Accordingly, it is another of the objects of my invention to provide an apparatus for centering the image reproduced on a cathode ray tube by means of a device which will be simple and highly practicable.

Accordingly, among the objects of my invention are:

To provide an apparatus which will eliminate some of the presently known hand adjusted controls in a television receiver. r

To provide an apparatus in which the centering of the image reproduced on the screen of a cathode ray tube is accomplished automatically.

To provide an apparatus for centering the image reproduced on a cathode ray tube by means of a device which will be simple and highly practicable.

My invention, in general, consists in providing spaced probes or conductors within the cathode ray picture tube or Kinescope, which have their extremities slightly outside the electron beam positions corresponding to the normal and visible picture range on the screen so that a deviation or shift of the picture from normal causes a development of a potential difference between pair of probes situated at opposite sides of the picture by the differential impingement of the cathode ray beam on the conductors or probes. This potential-difierence is utilized to develop a control bias potential or current which is applied to the corresponding deflecting means to supplement the normal fixed bias which is impressed thereon. The result then is that this variable bias acts to control the deflection of the cathode ray beam in such a manner that it is brought into a position where it will impinge equally onto the oppositely disposed pairs of conductors or probes, and hence the image will eiiectively have been drawn back onto its proper position on the fluorescent screen.

My invention will best be understood by reference to the figures in which:

Fig. 1 shows one embodiment of my invention using wire like probes.

Fig. 2 shows an arrangement for developing control voltages or currents in conjunction with the probe members.

Fig. '3 shows a method of applying the control potential to an electrostatic deflection system in conjunction with normal deflection potentials.

Fig. 4 is another embodiment in which the probes have appreciable width and depth.

Referring to Fig. 1, there is shownone em-, bodiment of my invention. In this figure a cathode ray tube having an envelope l0 contains an electron gun arrangement H and pairs of deflecting plates l2 and [3. At the end of the tube. remote from the electron gun structure, there is provided a fluorescent screen It, and the normal picture reproduction size is shown as bounded by the mask I9 which normally masks the area of the tube outside the limits of the viewed picture. Also positioned in the tube and adjacent the screen M are wire probe members 20, 22, and a pair ofprobes, one of which is indicated at 23,

and the seal through the glass envelope of the tube is indicated in the case of one of the wires at M. Appropriate lead-out members for each of the wire probes are provided.

The position of the electron beam of the tube is indicated in several positions after it has passed the deflecting plates of the tube, and such is indicated in dashed lines. The normal position of the beam in its extremities is indicated at 27, 28. It will be seen therefrom that the beam slightly impinges on the probe members 20 and 22 when the pictureie in. the normal position. For put poses of simplicity the position of the beam with respect to the remaining probes is not shown. However, it will be appreciated that since the wires are positioned along two axes which intersect at right angles, there is provided an arrangement wherein any position of the beam which lies outside the normal picture reconstructing position will be such that the beam will intersect more widely with one of the probes than with the probe immediately opposite thereto, since the probes are arranged in a fashion so that for normal picture reconstruction the beam in its extreme positions slightly and equally impinges upon the probe members, and the currents thereby set up will balance each other out in the corrective signal developing means which will be described hereinafter. However, should the extreme position of the beam vary it will be obvious that it will more widely contact with one of the probes than with the probe opposite thereto. illustrated by the position of the two dotted lines Rb and 26 wherein the position of the picture is such that it has risen from its normal centered position, and these two lines represent the upper and lower extremities thereof. Under such circumstances the beam wlil impinge further on the probe 22 than it impinges on the probe 2i), and hence a difference of potential between the probes will be created and a corrective signal will be developed by the apparatus such as illustrated hereinafter in Fig. 2. The action of the device is as follows:

The size'of the picture is adjusted in such. fashion that the picture boundaries fall slightly outside of the desired masked picture size, which is a favorable condition since the extreme edges of a picture are always somewhat distorted or irregular and therefore preferably are masked out. Accordingly, such a mask is provided as shown at if] in Fig. 1. The boundaries of the picture having been determined, if the picture is displaced too far to the right or to the left a difference of potential in one direction or the other will be developed between probes 2| and 23 by the differential impingement of the electron beam thereon. Similarly, if the picture is too far up or down a difference of potential will be developed between probes ill and 22. In either case a difference of potential between the horizontal probes as a pair, or the vertical probes as a pair may be utilized directly or indirectly to introduce deflection biasing potential in such a fashion as to neutralize the incorrect picture displacement and to carry the picture into a centered position, this being the position at which there will be no difference of potential between the horizontal probe pair or the vertical probe-pair. The essence of this arrangement, therefore, may be said to be that differences of potential developed between several probes within an optical image reproducing means are a function of the limits of a desired picture, and these probes control means for centering the picture in the direction of its deviation from a centered position, whether it be vertical or horizontal.

Referring to Fig. 2, there is shown an arrange- B ment for effecting the control of the movement of the picture which has deviated from the correct position. The probe members and 22 of Fig. 1 have been taken as illustrative, and for purposes of simplicity the remaining apparatus has been omitted from the tube. Probe member 22 is connected to the grid at of an amplifier tube ill having an anode 42, and a cathode it. The probe member so is connected to the grid it Such a condition is of a thermionic tube having cathode it) and anode W, the tube itself being identified as 5|. The cathodes of the two tubes Al and lil are shown as connected in parallel and are grounded. .The grid ii] is grounded through a resistor 58 and the grid M is grounded through resistor 59. These two resistors are of substantially equal values. The inner rectangle represents what may be a masked picture area.

Joining the anode M to the anode 60 is a resistor 52 and the center tap thereof is connected to the positive side of a supply potential 53, the negative terminal of which is connected to the cathodes t3 and M. The terminal of the resistor 52 which is connected to the anode M is connected to the grid 60 of an amplifying tube 6| having cathode 62 and anode 63. The terminal of the resistor 52 connected to the anode Bil is connected to the cathode 62 of the tube 6|. The anode 63 of tube 6! is connected serially through a resistor 64 and a deflection biasing source of potential 65 to the cathode 62. Voltages developed across the resistor (it may be taken off across the terminals 66 and 61. The operation of the device is as follows:

Unequal impingement of the cathode ray beam on the pair of probes will cause a change in the potentials of the grids of either tube M or 5| relative to each other. This means, then,'that 3.0 the plate current in the two tubes will be unequal and that a difference of potential will appear across the terminals of the resistor 52. This difference of potential may be amplified by impressing it across the grid cathode path of the amplifying tube GI and affecting the plate current of tube 6| so that there is developed a definite potential drop across resistor 64!. This potential may be impressed through appropriate coupling means onto the deflecting plates of the cathode ray tube as shown hereinafter in Fig. 3.

Referring to Fig. 3, there is shown one arrangement for impressing onto the deflection apparatus the developed bias potential which is to be used for corrective purposes. In this figure the normal deflection generator is illustrated as a schematic block showing and lead BI is connected to one of the deflecting plates 82 of a cathode ray tube 33. The other lead from the generator is connected to one terminal of a potentiometer arrangement comprising resistor 84 and having a slide arm arrangement 85. A source of potential 86 is shunted across resistor B l. The slide arm is connected to one terminal 8'! of a terminal pair t1 and 88, the terminal 88 being connected to the other deflecting plate 89 of the cathode ray tube 83. The potentials developed across resistor M of Fig. 2 may then be impressed onto terminals ill and 38 through appropriate and well known coupling means. The contact 35 60 may be set initially for centering with each tube.

to in two coordinates of motion.

The deflection controls are then set so that the picture is slightly too large in each dimension Thereafter, if the picture shifts off center potential differences will develop between the vertical 5 probe pair or between the horizontal probe pair,

and in each case will provide an additional bias for moving the picture by means of changing the bias on the deflecting means in the cathode ray tube.

Referring to Fig. 4, there is shown an alternative arrangement of my invention. In this figure the cathode ray tube envelope 30 contains an electron gun structure 3! and electrostatic defleeting means 32 and 33 for deflecting the beam In this figure the probe members are planar conducting plates 34, 35, 36 and 31, and it will be seen from the dotted line 38 that the edge of these plates marks or frames slightly more than the picture of the desired size, the unmasked pictures size being shown at 39, and the normal picture extremities masked being indicated at 29. As in the previous illustration, appropriate lead members are provided for passing through the tube wall to the exterior thereof for purpose of connection to other apparatus. The probes should be made preferably of a material inherently having a small secondary electron emission. Such materials as graphite coatings or the like on the probe membets are appropriate.

The centering control system shown in this application is not affected by symmetrical increases or decreases in the size, but only as a result of decentering of the picture. For instance, inthe initial adjustment by the user the picture may be made slightly larger in each dimension than the viewed area, which is done easily by merely bringing it to the viewed area and then turning the picture size control knobs by a given amount which is adequate to immerse the probes in the scanning beam outside the viewed picture area. Instructions to the user of the receiver may indicate approximately how much turning of the knob is required for this purpose.

It is further possible to arrange the circuits so that if any probe falls to zero potential the amplitude of the deflection generator voltage or current may be increased suitably. It will be apparent to those skilled in the art to which this invention belongs that there maybe deviations from the particular showing thereof which will fall purely within the spirit and scope of my invention and will be the equivalent thereof, and I am entitled to such deviations from the particular showing as are the equivalent thereof and that fall fairly within the scope of the hereinafter appended claims.

What I claim is:

1-. The method of controlling the position of the image reproduced on the viewing target of a cathode ray tube which comprises the steps of flxing the normal image position, developing corrective signals in accordance with the deviation of the instantaneously produced image from the normal image reproducing position and utilizing the developed corrective signals automatically to return the produced image to its normal position.

2. Apparatus for controlling the position of the image reproduced on a cathode ray tube screen comprising a cathode ray tube having an anode and a cathode for developing an electron beam, a 7

target to receive the developed electron beam, and deflecting means to cause said beam to trace a pattern of predetermined size on the target and beam intercepting electrodes intermediate the beam deflecting means and the target for developing signals from the impingement of the beam on said intercepting electrodes, and means for modifying the deflection of said beam under the control of said developed signal.

3. Apparatus in accordance with claim 2, wherein said. intercepting electrodes comprise at least a pair of wire probe members.

4. Apparatus in accordance with claim 2, wherein said intercepting electrodes comprise at least a pair of planar members.

5. In apparatus for controlling the position of the reproduction or an electro-optical image on the viewing target of a cathode ray tube wherein there are included electron beam forming electrodes for developing a cathode ray beam to impact the target and means for deflecting the said electron beam across the target to produce a scanning raster of which the extremities of the normal path of the said developed beam are redeterminedly and substantially fixed in position, a plurality of electrically opposing beam in tercepting electrodes located intermediate the beam deflecting means and the target and normally protruding into the path of the said deflected electron beam so that electrical energy is developed at the intercepting electrodes during periods of beam impact thereupon, means for developing electrical energy of substantially equal magnitude by the impact of the electron beam upon the opposing intercepting electrodes for normal image reproduction and electrical energy of unequal magnitudes for image reproduction varying from the selected normal to produce corrective signals in accordance with the unequal magnitude developed energies, and means for applying the produced corrective signals to the respective deflecting means for restoring the scanning raster to a normal location.

6. In apparatus for controlling the position of the reproduction of an electro-optical image on the viewing target of a cathode ray tube wherein there are included electron beam forming electrodes for developing a cathode ray beam to impact the target and means for deflecting the said electron beam across the target to produce a scanning raster of which the extremities of the normal path of the said developed beam are predeterminedly and substantially fixed in position, masking means to limit the observable area of the produced raster to a fractional-part of the total raster traced, a plurality of pairs of electrically differential and opposing beam intercepting electrodes located intermediate the beam defleeting means and the target, said pairs of electrodes terminating within the volume lying between the volume formed' between the outer boundaries of the normal raster and the point at which the deflecting means is effective to deflect the beam and that volume formed between the boundaries of the unmasked raster and the said point so that the said beam impacts the said electrodes within the time period required to trace the masked portion of the raster, means for developing by the impact of the electron beam upon the intercepting electrodes electrical energy of substantially equal magnitude on the opposing intercepting electrodes for normal image reproduction and electrical energy ofunequal magnitudes for variant image reproduction to produce corrective signab in accordance with the unequal magnitude of the developed energies, and means for applying the produced corrective signals to the respective deflecting means for restoring the scanning raster to a normal location.

7. Apparatus in accordance with claim 5, wherein said intercepting electrodes comprise two pairs of planar conducting members, the

transverse axis or one of said pairs of members I being positioned substantially at right angles to the transverse axis of the other of said pairs of members.

8. Apparatus in accordance with claim 5, wherein saidv intercepting electrodes comprise tour electrodes spaced .apart substantially a quadrant.

ALFRED N. GOLDSMITH. 

